1. Field of the Invention
The present invention relates generally to medical devices and, more particularly, to sensors used for sensing physiological parameters of a patient.
2. Description of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the field of medicine, doctors often desire to monitor certain physiological characteristics of their patients. Accordingly, a wide variety of devices have been developed for monitoring many such physiological characteristics. Such devices provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, such monitoring devices have become an indispensable part of modern medicine.
One technique for monitoring certain physiological characteristics of a patient is commonly referred to as pulse oximetry, and the devices built based upon pulse oximetry techniques are commonly referred to as pulse oximeters. Pulse oximetry may be used to measure various blood flow characteristics, such as the blood-oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and/or the rate of blood pulsations corresponding to each heartbeat of a patient. In fact, the “pulse” in pulse oximetry refers to the time varying amount of arterial blood in the tissue during each cardiac cycle.
Pulse oximeters typically utilize a non-invasive sensor that transmits light through a patient's tissue and that photoelectrically detects the absorption and/or scattering of the transmitted light in such tissue. One or more of the above physiological characteristics may then be calculated based upon the amount of light absorbed or scattered. More specifically, the light passed through the tissue is typically selected to be of one or more wavelengths that may be absorbed or scattered by the blood in an amount correlative to the amount of the blood constituent present in the blood. The amount of light absorbed and/or scattered may then be used to estimate the amount of blood constituent in the tissue using various algorithms.
Two categories of pulse oximetry sensors in common use may be classified by their pattern of use: the disposable and the reusable sensor. Disposable sensors are typically flexible bandage-type structures that may be attached to the patient with adhesive materials, providing a contact between the patient's skin and the sensor components.
Occasionally, healthcare workers may inadvertently use a flexible, disposable sensor indicated for one tissue site on a tissue site for which the sensor is not designed. For example, a sensor designed to fold around the tip of a digit may be mistakenly placed flat on the forehead of a patient. A digit sensor may be arranged in a transmission-type configuration, with the sensing elements designed to lie on opposing sides of the tissue. Laying such a sensor flat against the skin on the forehead in a reflectance-type configuration, with the sensing elements side-by-side, may contribute to measurement inaccuracies. The sensing elements may have been calibrated for transmission-type use, and may not operate correctly when applied in a reflectance-type configuration.
Sensor misplacement may also contribute to a poor fit of the sensor against the tissue, as a digit sensor may be too large or heavy to be supported by its adhesive on the forehead, and thus may be easily dislodged by patient movement. Further, the relatively large surface area of a digit sensor may not conform to the curved surface of the forehead, and thus may be susceptible to signal artifacts associated with movement of the sensor relative to the tissue. Additionally, signal artifacts may be associated with a poor fit of the sensor against a patient's tissue. An ill-fitting sensor may allow ambient light to reach the detecting elements of the sensor, which may also interfere with the amount of light detected. An ill-fitting sensor may also be more susceptible to mechanical deformation than a sensor that is tightly adhered to the skin.